The present application relates generally to an improved data processing apparatus and method and more specifically to mechanisms for resolving multiple patterning conflicts.
Optical lithography is a crucial step in semiconductor manufacturing. The basic principle of optical lithography is quite similar to that of chemistry-based photography. The images of the patterned photo-mask are projected through the high-precision optical system onto the wafer surface, which is coated with a layer of light-sensitive chemical compound, e.g. photo-resist. The patterns are then formed on the wafer surface after complex chemical reactions and follow-on manufacturing steps, such as development, post-exposure bake, and wet or dry etching.
Multiple patterning is a class of technologies developed for photolithography to enhance the feature density. The simplest case of multiple patterning is double patterning, where a conventional lithography process is enhanced to produce double the expected number of features. Double exposure is a sequence of two separate exposures of the same photoresist layer using two different photomasks. This technique is commonly used for patterns in the same layer which look very different or have incompatible densities or pitches. In one important case, the two exposures may each consist of lines which are oriented in one or the other of two usually perpendicular directions. This allows the decomposition of two-dimensional patterns into two one-dimensional patterns which are easier to print.
Double pattern lithography (DPL) is an effective technique to improve resolution. DPL theoretically doubles resolution through pitch splitting. DPL involves two separate exposure and etch/freeze steps (litho-etch-litho-etch or litho-freeze-litho-etch). DPL is expected to be needed for 20 nm technology and is one of the best candidate solutions for scaling to 14 nm technology and beyond.
Layout decomposition includes mask assignment, also referred to as graph coloring. In one case, shapes to be formed using photolithography are colored such that two shapes within a predetermined distance are colored differently, meaning they are formed using different photographic masks. Shapes of different masks can overlap. The point at which masks overlap is referred to as a stitch. Stitching is used to resolve a coloring conflict; however, not all conflicts can be resolved by stitching. Some conflicts require layout perturbation or modifications.
In one prior art solution, one may construct a conflict graph, detect odd cycles, and perform wire perturbation. One may repeat this process iteratively until no improvements are possible. Wire perturbation comprises finding all possible perturbations to resolve a conflict and perform trial compaction. This solution has a very long runtime. Also, using this solution, it is impossible to cover all combinations of perturbation. This solution does not consider impact on cross layer constraints like via coverage, etc. A resolution of one conflict may introduce other conflicts. In addition, this solution only works with a single spacing rule and cannot be used with shape-dependent design rules.
In another prior art solution, one may pre-compute all wire-spacing options that reduces conflicts. This solution formulates coloring problem as integer linear programming (ILP) to minimize candidate wire-spreading options. This solution is very slow. This solution is limited to wire-spreading, and spreading may cause new conflicts at other places.
Another solution uses split level design for double pattern lithography. The solution specifies a DPL layer as two layers. For example, a metal layer, M1, is specified to the designer as M1a and M1b corresponding to two exposures of DPL. The designer must then consider inter- and intra-level ground rules to ensure DPL compatibility during design. This solution exposes the designer to DPL such that the designer must ensure the design satisfies extra design rules for DPL compatibility.
The prior art solutions present trade-offs between “correct-by-construction” and “layout legalization” approaches. Correct-by-construction exposes designers to DPL complexity. Layout legalization flows are runtime intensive and suffer from the issue that resolution of one conflict may create other conflicts. A conflict removal flow should shield designers from DPL complexity and provide efficient flow that detects and fixes conflicts once and for all simultaneously across all layers.